It has been hitherto known that oxides are used for cutting tools, wherein oxide films mainly composed of aluminum oxide (alumina) are formed predominantly according to a CVD method (chemical vapor deposition method). The CVD method cannot be employed for tools whose blade edge is sharp or axle tools because the treating temperature upon the formation is generally as high as 1000° C. or over and thus, studies have been made on formation techniques by a PVD method (physical vapor deposition method). In Japanese Patent Publication No. 3323534, there has been proposed a method of forming (Al, Cr) oxides by a PVD method. In Japanese Laid-open Patent Application No. 2002-544379, there is described a method wherein γ-alumna is formed on a tool according to a pulse sputtering method.